Broadband magic t



Jan. 14, 1958 B. E. WALLACE, JR

BROADBAND MAGIC T Filed Feb. 16, 1956 INVENTOR BERT E WALLAGEJR.

ATTORNEYS United States BROADBAND MAGIC T Application February 16, 1956, Serial No. 566,056

Claims. (Cl. 333-11) The present invention relates to a broadband magic T and more particularly to a broadband magic T having stubs for matching purposes.

Where any abrupt change in structure occurs in a wave guide, mismatch and consequent undesirable reflections are produced, but if a wave guide is terminated in its characteristics impedance there are no reflections. A magic T in a rectangular wave guide system consists of an H-plane T (i. e., a parallel or H arm joined to a main wave guide) and an E-plane T (i. e., a series or E arm joined to a main wave guide) wherein both Ts have the same main wave guide and the axes of the H arm and E arm coincide with the axis of the main wave guide at the same point. It is evident that the magic T junction is a severe change in structure for the branch arms (H arm and E arm) and if reflections in these arms are to be avoided some type of matching device will have to be employed. Matching of this junction in the past has usually been accomplished by means of a post in the H arm and an iris in the E arm. Thereby, the H arm is made reasonably broadband; however, the E arm is somewhat frequency sensitive,

but the main drawback to this scheme is the limitationv on the amount of power that can be transmitted, for under high power conditions voltage breakdown occurs across the matching elements, i. e. across the post and iris.

In the present magic T, matching is obtained through the addition of a series stub to the H arm and a parellel stub to the E arm. Thus, there are no projections within the wave guides and the power handling capabilities of the magic T is limited only by the dimensions of the wave guides. This devices can be made very broadband and also there is less dissymmetry than with conventional systems.

Accordingly, an object of the present invention is the provision of a magic T in which the H arm and E arm are matched.

Another object is to provide a broadband magic T having a power capacity that is limited only by the dimensions of the wave guides that make up the magic T.

A further object of the invention is to provide a broadband magic T having very little dissymmetry.

Other objects and many of the attendant advantages of this invention will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawing wherein the sole figure is a perspective view of a preferred embodiment of the magic T junction of this invention.

atent 0 "ice Referring now to the drawing there is shown in the figure a magic T comprising a main wave guide 11 to which there is connected an E arm 12 and an H arm 13. A parallel stub 14 is joined to the E arm 12 and a series stub 15 is joined to the H arm 13. The stubs can be soldered in position and could be made adjustable in length by means of a plunger, but in production units, for optimum performance at any specific frequency within the band, the stubs would be fixed for the particular wave guide size. As is well known in the art, the stubs act either as series or parallel resonant circuits and thereby render the junction impedances seen by the arms equal to the characteristic impedances of the arms, and thus eliminate the reflections that would otherwise be present. The exact size and placement of the matching stubs depend upon the frequency band to be covered and the size of the wave guide, and can readily be found by one skilled in the art through use of the Smith chart and well-known empirical procedures.

Obviously many modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.

What is claimed is:

1. A broadband magic T comprising: a main wave guide, an H arm connected to said main wave guide so that the axes of the H arm and main wave guide intersect at a point, an E arm joined to said main wave guide so that its axis passes through the point of intersection of the axes of said H arm and main wave guide, a series stub joined to said H arm, and a parallel stub joined to said E arm.

2. The broadband magic T of claim 1 wherein the size and placement of said series stub is such that said H arm is terminated in its characteristic impedance at the magic T junction.

3. The broadband magic T of claim 2 wherein the size and placement of said parallel stub is such that said E arm is terminated in its characteristic impedance at the magic T junction.

4. In an electromagnetic wave guide structure including a main wave guide and two branch wave guides joined thereto to form a junction having series and parallel arms respectively extending therefrom, parallel stub means joined to said series arm adjacent said junction for matching the impedance of said junction to said series arm and series stub means joined to said parallel arm adjacent said junction for matching the impedance of said junction to said parallel arm.

5. In a magic T comprising a main wave guide and an H arm and an E arm joined, a device for matching the impedance of the magic T junction to the characteristic impedance of said H arm and E arm comprising stub means symmetrically joined to said H arm and E arm.

References Cited in the file of this patent UNITED STATES PATENTS 2,685,065 Zaleski July 27, 1954 

